1. Field of the Invention
The present invention relates to an exhaust muffler structure for an internal combustion engine, and more particularly to an exhaust muffler structure for an internal combustion engine such as an air-cooled two-cycle gasoline engine used for working machine like a mower and a chain saw.
2. Description of the Related Art
In recent years, in an internal combustion engine such as an air-cooled two-cycle gasoline engine for a mower and a chain saw also, it has been demanded to provide an oxidizing catalyzer in a muffler to reduce HC (hydrocarbon) content, CO (carbon monoxide) content and the like in combustion gas exhausted from the engine and to purify the exhaust gas.
The present applicant proposed an exhaust muffler structure for an internal combustion engine which was disclosed in the specification of Japanese Utility Model Laid-Open No. Heisei 3-92517 filed prior to the present application. In this exhaust muffler structure, a cylindrical member of which cloth catalyzer is formed by adhering oxidizing catalyzer to a cloth-shaped base material is disposed in the exhaust muffler in such a manner that an exhaust gas guide cylinder is enclosed by the cylindrical member. FIGS. 6 and 7 show such conventional exhaust muffler structure for an internal combustion engine as described above. FIG. 6 is a lateral cross-sectional view showing a primary portion of the conventional exhaust muffler which is attached to a main body of the internal combustion engine, and FIG. 7 is an exploded perspective view of the exhaust muffler illustrated in FIG. 6.
In FIGS. 6 and 7, a heat insulating plate 11 is mounted between the internal combustion engine 20 and the exhaust muffler 10 to prevent heat of the exhaust muffler 10 from transiting to the internal combustion engine 20 and a fuel tank 29, and to guide cooling air in combination with a cylinder cover 27. The exhaust muffler 10 is divided at a lateral joining face 10c into two pieces, an inner exhaust muffler half 10a on the side of the main body of the internal combustion engine 20 and an outer exhaust muffler half 10b. In the above-mentioned inner exhaust muffler half 10a, an exhaust gas guide cylinder 13 and a pair of supporting posts 14 and 15 positioned in parallel to the cylinder 13 on both sides thereof. The exhaust muffler guide cylinder 13 is fixed to an inner reinforcing plate 28 which is attached to an inner wall of the inner exhaust muffler 10a. A communication hole 16 communicating with the inner reinforcing plate 28 and the exhaust gas guide cylinder 13, an exhaust hole 17 formed on the heat insulating plate 11, and an exhaust port 25 on the side of the main body of the inner combustion engine 20 are in communication with each other. Further, a plenty of small holes 18 are formed on a peripheral wall of the exhaust gas guide cylinder 13 to communicate the inside and outside of the engine 20 with each other.
Stud bolts 21 and 22 projecting from both sides of the exhaust port 25 on the side of the internal combustion engine 20 are inserted into the communication holes of the supporting posts 14 and 15 and the communication hole of the outer exhaust muffler half 10b in this order, and nuts 23, 24 are engaged with tips of the stud bolts 21, 22, which causes the inner and outer exhaust muffler halves 10a and 10b to be integral with each other and sealed. Further, an exhaust muffler cover 26 is detachably mounted on the side of the main body of the internal combustion engine 20.
When integrally combining the inner and outer exhaust muffler halves 10a and 10b, a substantially cylindrical member 30 of which cloth catalyzer is supported between two wire nets is deformed to a substantial ellipse in such a manner that the exhaust gas guide cylinder 13 is enclosed by the cylindrical member 30, and the cylindrical member 30 is sustained between a pair of the supporting posts 14 and 15.
With the construction described above, exhaust gas generated by the operation of the internal combustion engine is extracted from the exhaust port 25 of the internal combustion engine 20 to the exhaust gas guide cylinder 13 of the exhaust muffler 10. Then, the exhaust gas passes through the small holes 18 of the exhaust gas guide cylinder 13 and further passes through the cloth catalyzer of the cylindrical member 30 to finally be extracted from an exhaust pipe 40 to open air.